InternetNews talks to developers and vendors about the rise of Btrfs as a successor to Ext4. Though Ext4 adds extents, Chris Mason, Btrfs developer noted that BTRFS adds a number of other features beyond that. Among those features are items like snapshotting, online file consistency checks and the ability to perform fast incremental backups. BTRFS (pronounced better FS) is currently under development in an effort led by Oracle engineer Chris Mason. With the support of Intel, Red Hat, HP, IBM, BTRFS could become the engine that brings next generation filesystem capabilities to Linux.

ZFS is licensed under CDDL. This license is GPL incompatible and apparently deliberately designed to be so, because some of Sun folks were worried about losing their technology to Linux and some developers threatened to quit if their work was put under GPL (by far the most used foss license. refer http://www.dwheeler.com/essays/gpl-compatible.html ).

Linux developers cannot possibly just take code and ignore the licensing incompatibility. So they are being prudent and implementing things from scratch in Linux taking advantage of existing Linux kernel API including the vfs and block layer. Yes, it is unfortunate that license incompatibility between free and open source software prevents it from being reused but when vendors do it deliberately, not much can be done about it

There is also the little question about who actually invented ZFS. Sun and NetApp are in a lawsuit over the patents on the file system right now. Even if Sun licensed ZFS as GPL, it would be pretty dumb to put it into the kernel until the legal questions are settled.